The present invention is related to a magnetic field sensor, and more particularly to a mixed anisotropy magnetoresistive sensor.
Sensors are generally known for measuring the magnitude of a magnetic field based on either giant magnetoresistive (GMR) or tunneling magnetoresistive (TMR) materials. These materials are typically made up of two ferromagnetic thin films separated by a non-magnetic spacer. In most applications, one of the magnetic layers is “pinned,” holding the orientation of the magnetization of that layer in a fixed direction. The other layer is free to rotate from an equilibrium direction, usually dictated by the coupling between layers as well as the shape in which the magnetic layers are patterned. The degree of deviation of the free layer is proportional to the amount of external field the sensor is exposed to, up to a saturation field (HS). The changes in relative orientations of the magnetizations of the pinned and free layers cause a corresponding change in the measured resistance when current flows through the sensor. FIG. 1 is a graph illustrating this resistance versus applied field curve, with layer orientations inset therein.
If the non-magnetic spacer separating the ferromagnetic thin films is made of a conductive material, the sensor is a GMR sensor. If the non-magnetic spacer separating the ferromagnetic thin films is an insulating material, an added gain in magnetoresistance (MR) change is observed due to quantum mechanical tunneling of spin polarized current, and the sensor is a TMR sensor.